The invention relates to communications, and has applicability to Metropolitan Area Networks according to the IEEE 802.16 WirelessMAN standard.
In a typical communication system architecture, users are coupled for communication to one or more nodes, such as base stations, which, in turn, are coupled for communication to public communication networks such as the Internet. Communication streams between such users pass through their respective base stations, and across the public networks.
Such communication streams are multiplexed within distinct frequency bands through techniques such as Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA). For instance, implementations of OFDMA include a physical (PHY) layer, and employ subcarriers having complex symbols (that is, symbols that include both real and imaginary components, and therefore can be characterized as having a phase). The complex symbols are modulated using a PseudoRandom Bit Sequence (PRBS), which is generated from a seed value using PRBS generator register circuitry.
A user will employ an implementation of PRBS generator register circuitry, and of seed values. The user may develop the implementation him/herself, or may obtain it from a vendor. For instance, as the 802.16 standard becomes more accepted and commonplace, different implementations will become available from different vendors. Most such implementations will be in the form of 802.16e-OFDMA PHY chip designs. Such designs typically are highly integrated; that is, the PRBS function is integrated with the rest of the modulator, so it is probably done independently by each chip manufacturer.
In order for communication to take place between different users, their respective implementations of the seed value and the PRBS generator register circuitry should be interoperable. Failure to communicate can be due to lack of such interoperability. Therefore, it is desirable that, for a given implementation of an OFDMA transmitter, interoperability with other implementations can be verified.
Conventionally, interoperability verification of PRBS generator implementations (in particular, implementations of the PRBS generator register circuitry and the seed values) has been done ad-hoc and manually. The ad-hoc check has been done when interoperability problems or questions arise. A comparison is done between two implementations (usually the symbol bit output generated from a given PRBS seed) and then differences between them are identified (either in the filling of the PRBS register, or in the sequence output). This manual approach required working across implementations for comparison without independent verification. It also has required cooperation between different service provider companies, or between different hardware vendors.
Such conventional verification has been disadvantageous, among other reasons because the necessary cooperation between different companies may not always be available, and because the lack of independent verification makes it difficult to ensure interoperability proactively. Rather, interoperability problems can only be solved reactively, in response to observed communication problems.